Thermoplastic pavement markings are commonly used for directing vehicle traffic. The markings are durable, retroreflective, and, when applied on asphalt road surfaces in a molten state to the surface of the road, they cure quickly to a solid state. This allows the road to be opened to traffic sooner than pavement markings that are required to dry or chemically cure. The prior art markings usually comprise a reflective portion (typically glass spheres), a binder portion (resins, waxes, plasticizing oil, polymers), a pigment portion, and a filler portion (usually calcium carbonate). The most common form (and least expensive) of this product is a dry blend of all the ingredients. This dry blend method has a cost advantage, but final the product can be dusty, the filler portion can absorb moisture, and the dry blend usually takes longer to melt as the resins, polymers, and waxes have to melt and be absorbed by the filler portion to liquefy. This process usually additionally requires a significant amount of agitation of the mixture.
There are other forms of prior art pavement markings that have reduced the dust and melt speed by pre-melting the material and cooling it. One such form of manufacturing is block form, where the materials of the markings are is blended and heated to a molten state, poured into wax or fluoropolymer release coated boxes and allowed to cool. Although material supplied in this form is less dusty and does not absorb as much moisture, it usually must to be broken up into pieces in order to melt quickly, and is therefore labor intensive.
Another form of the pavement markings is pelletized. Pelletized thermoplastic markings are less dusty, absorb less moisture, and are less labor intensive. However, they are expensive to manufacture and require costly equipment. The raw ingredients usually are melted, extruded, cut into pellets, and to keep the pellets from remassing in storage, they are coated with a release coating in a subsequent process. The glass beads can be damaged in some extrusion/pelletizing processes which also leads to premature wear of equipment parts. The amount of bead damage could also cause the product to not meet certain specifications for bead gradation.
Accordingly, there is a need to address the aforementioned deficiencies and inadequacies of the prior art pavement markings. New methods and compositions to create free flowing thermoplastic materials for road markings that reduce dust, moisture absorption, and labor in addition to minimizing cost and production effort are desired.